We propose to study the mechanism of activation of human plasminogen by urokinase. The rationale to be used is to attempt to selectively inhibit the enzymatic activity of the generated plasmin while not inhibiting the enzymatic activity of the activator, urokinase. We will compare the activation products obtained with those obtained in the activation with no inhibitor present by protein physical and chemical methods. Coupling this information with kinetic measurements will allow an understanding of the activation mechanism of human plasminogen. We are also interested in studying the structural requirements of the bacterial plasminogen activator, streptokinase, necessary for activation of human plasminogen. During the coming year, we will prepare and characterize various streptokinase fragments and determine their plasminogen activating capabilities. BIBLIOGRAPHIC REFERENCES: Siefring, G.E., Jr., and Castellino, F.J., De Novo Biosynthesis of Plasminogen in the Anephric Rat, J. App. Physiol. 38, 114-116 (1975). Castellino, F.J., Sodetz, J.M., and Siefring, G.E., Jr., Affinity Chromatography Resolution of Plasminogen Isozymes, Isozymes. I. Molecular Structure, C.L. Markert, Ed., Academic Press, New York, p. 245-258 (1975).